Rise in chloroform emissions threatens ozone layer

MIT study shows increase of ozone-depleting chloroform emissions in East Asia, which could slow recovery of the ozone layer by four to eight years.

Image of the largest area of Antarctic thinning ever recorded, in September 2000

Courtesy of NASA via Wikimedia Commons

An MIT study published last month in Nature Geoscienceidentifies chloroform – used in the manufacture of R22 – as a threat to the recovery of the ozone layer, according to the MIT News Office.

The researchers found that between 2010 and 2015, emissions and concentrations of chloroform in the global atmosphere have increased significantly. They traced the source of these emissions to East Asia.

The researchers predict that if chloroform emissions continue to increase, the recovery of the ozone layer – made possible by the phase out of CFC and HCFC gases via the Montreal Protocol – could be delayed by four to eight years.

“[Ozone recovery] is not as fast as people were hoping, and we show that chloroform is going to slow it down further,” says co-author Ronald Prinn, the TEPCO Professor of Atmospheric Science at MIT. “And certainly a conclusion here is that this needs to be looked at.”

Xuekun Fang, a senior postdoc in Prinn’s group, is the lead author of the paper, which includes researchers from the United States, South Korea, Japan, England, and Australia.

Chloroform is among a class of compounds called “very short-lived substances” (VSLS), for their relatively brief stay in the atmosphere (about five months for chloroform). Because it is generally assumed that chloroform and other VSLSs are unlikely to do any real damage to ozone, the Montreal Protocol does not stipulate regulating the compounds.

Prinn, Fang, and their colleagues monitor such compounds, along with other trace gases, with the Advanced Global Atmospheric Gases Experiment (AGAGE) — a network of coastal and mountain stations around the world that has been continuously measuring the composition of the global atmosphere since 1978.

Using an atmospheric model, Fang and his colleagues estimated that between 2000 and 2010, global chloroform emissions remained at about 270 kilotons per year. However, this number began climbing after 2010, reaching a high of 324 kilotons per year in 2015. Fang observed that two stations in East Asia — one in Hateruma, Japan, and the other in Gosan, South Korea — showed dramatic increases in the frequency and magnitude of spikes in the ozone-depleting gas.

In November 2018, an assessment of ozone depletion in the atmosphere concluded that actions taken under the Montreal Protocol have led to decreases in the atmospheric abundance of controlled ozone-depleting substances (ODS) and the start of the recovery of stratospheric ozone.

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[Ozone recovery] is not as fast as people were hoping, and we show that chloroform is going to slow it down further.” – Ronald Prinn, MIT